Matsuzaka had been thriving at Vegas ever since Jenrry Mejia beat him out for the Mets' fifth-starter job, posting a 2.25 ERA in two Triple-A outings.

"I actually expected to be in Vegas for longer, so this is pretty much out of the blue," Matsuzaka said through his interpreter. "But I'm glad. The earlier, the better, so I'm pretty happy about that."

The move serves two purposes for the Mets. In the short-term, it gives them the legitimate long man that they thought Lannan could be out of their bullpen -- before the lefty gave up seven runs in his first four innings.

It also provides the Mets with some bona fide rotation insurance should one of their other pitchers miss a start. Mejia is nursing a blister on his right middle finger, and though the Mets expect him to make his next start Monday, that is no guarantee. Bartolo Colon has also been dealing with a back issue that the Mets consider minor.

"Right now, we brought up Daisuke to pitch out of the 'pen, more or less in a long role," general manager Sandy Alderson said of Matsuzaka, who has made one professional relief appearance since coming to the U.S. seven years ago. "But he does give us some insurance with any of our starters, frankly, if they need to miss one or get backed up a little."

"Coming out of the bullpen is definitely something new to me, but I understand what's expected," Matsuzaka said. "I'll just have to do the best I can and pick things up as I go along."

As for Lannan, the left-hander has 72 hours to decide whether to accept an assignment to Las Vegas or become a free agent. Lannan said he planned to take that time to talk to his agent, discuss his options and make a decision.

"The team's doing really well and I wasn't really contributing, so they had to go in a different direction," Lannan said. "I completely understand. It's back to the drawing board."

Anthony DiComo is a reporter for MLB.com. Follow him on Twitter @AnthonyDicomo. This story was not subject to the approval of Major League Baseball or its clubs.